A planetary steering differential which has been particularly effective for continuously driving the opposite output members of a track-type tractor at equal speeds for straight-ahead operation, or at different speeds for steering operation is disclosed in U.S. Pat. No. 4,434,680 issued Mar. 6, 1984 to C. W. Riediger, et al. However, the planetary steering differentials disclosed in that patent are not as compact as desired, and have a number of assembly, disassembly and serviceability disadvantages. One disadvantage resides in the orientation of the steering motor and associated input pinion on a horizontal, transverse axis. With such orientation, the steering motor is relatively inaccessibly located within the vehicle case and it is difficult to service it or the associated hydraulic lines connected to it. One solution to this resides in mounting the steering motor in a radial orientation external to the vehicle case as is disclosed in U.S. Pat. No. 4,557,157 issued Dec. 10, 1985 to E. D. Oestmann. But while the steering motor is accessible in that solution, major portions of the steering differential are added to the vehicle case through different openings so that considerable service time is required for assembling or disassembling the remainder thereof.
Another disadvantage with the steering differential of U.S. Pat. No. 4,434,680 is that the planetary steering differential is partly assembled or disassembled within the vehicle case by a mechanic leaning through an access opening. Still another problem is that it is difficult to disconnect the opposite axle shafts in order to allow removal of the planetary steering differential located therebetween.
Accordingly, what is needed is a compact planetary steering differential having a radial orientation of the steering motor at an external accessible location, and an efficacious mounting arrangement for rotatably supporting the elements of the planetary steering differential so that the majority thereof can be handled as a modular assembly capable of being easily connected to the vehicle frame. Specifically, it is preferred that the two bevel gear and pinion sets thereof be preadjusted in an effective manner as a subassembly before installation on the vehicle.
The present invention is directed to overcoming one or more of the problems as set forth above.